Why does a 3D solid become difficult to edit after using UNION?

[indiancad]

Have you ever combined several 3D solids with UNION, only to find that editing one particular part later becomes difficult?

Once separate solids are united, AutoCAD treats them as a single 3D solid. If you still need to modify individual components, I prefer keeping the original solids or using SLICE when I need to separate a specific portion.

For complex models, combining everything too early can make later changes harder.

How do you usually manage 3D solids when you know the model will need revisions later?